Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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820 FXUS66 KMTR 020926 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 226 AM PDT Tue Jul 2 2024 ...New SYNOPSIS, SHORT TERM, LONG TERM... .SYNOPSIS... Issued at 1258 AM PDT Tue Jul 2 2024 A significant and prolonged heat wave begins today and will last through the weekend. Inland areas will have dangerous record breaking heat this week. Red Flag Warnings are in effect for some higher elevations due to low humidity and gusty offshore winds. Skip the fireworks this year. Wildfires will be easy to start and quick to spread. && .SHORT TERM... (Today and tonight) Issued at 1258 AM PDT Tue Jul 2 2024 The high pressure dome is building, causing the marine layer to compress. Most areas will start the day cloud-free, though some areas along the immediate coast or northern Salinas Valley may have some fog or mist during the morning commute. Temperatures are already 5-10 degrees warmer than 24 hours ago, and that trend will accelerate after sunrise. Some inland areas will reach the 90s by 11 AM and 100s before 1 PM. The max temperature forecast has increased by a degree or two for most of the area. San Francisco will have a sharp gradient across the city with mid to upper 80s expected Downtown, and mid 60s at Ocean Beach. San Jose has a 40% chance of reaching 100 degrees today. The Red Flag Warning recently began, and wind gusts of 15-30 mph have already been observed in the mountains this morning. Low temperatures tonight will be several degrees warmer than they are currently, and well above average with many inland areas remaining in the upper 60s or low 70s. There won`t be much relief overnight. && .LONG TERM... (Wednesday through Monday) Issued at 1258 AM PDT Tue Jul 2 2024 The record breaking heat isn`t going anywhere. The high pressure dome will linger over California for at least a week, with more long range guidance suggesting that timeline may even be optimistic. A very slow moving ridge of high pressure is causing air to descend. Descending air warms and dries on the way down. This leads to cloud free skies and hot, dry air at the surface. Fortunately, as the high pressure gradually meanders east and becomes centered directly over California, the moderate offshore winds will abate by mid week as gentle onshore flow returns. This will help with fire weather concerns and allow coastal areas to cool off a bit. However, with the strong high pressure in place, these onshore winds will only cool off areas very close to the coast, as the marine layer will remain compressed under 1,000 ft. The temperature ticked up a degree or two with the updated forecast for most areas. The deterministic NBM is well below the mean, especially for max temps in coastal areas such as San Francisco and Santa Cruz. The difference is less obvious for inland areas, but still noticeable. The forecast leans heavily towards the ensemble mean, rather than the deterministic NBM, based on past performance during similar heat waves. The overall message is the same, inland areas will have dangerous heat extending through the weekend at least. The previous discussion mentioned that we have a chance to break the all-time record temperature at 850mb (roughly 5,000 ft) measured by the OAK weather balloon this weekend. The current record is 31C with observations dating back to 1948. While that remains a possibility, another important point to demonstrate the length of this heat wave is the amount of time we are expected to stay above 25C at 850mb. This threshold is only reached 1.8% of the time, so we`ll call it the 98th percentile of low level atmospheric temperatures. With greater than 90% certainty, the current GEFS and ECMWF ensembles predict that we will climb above the 98th percentile Tue or Wed, and reamin above this threshold for at least 6 days. At that point the GEFS shows a 10% chance of dipping below 25C, but on the flip side, there is also a 10% chance of a new all time record of 32C at that time. This spread demonstrates that the confidence is certainly lower next week, but the most likely timeline for relief (when the ensemble means dip below the 25C) doesn`t occur until Saturday the 13th. That`s 12 days in the 98th percentile of 850mb temps. *While we have all seen temperatures like this before, this event may end up approaching the upper end of what we`ve seen historically, in terms of longevity. Heat is the #1 weather- related killer in the United States. This is a significant heat wave, especially for inland areas. Please take the proper precautions, as impacts will only worsen day-by-day. A bit on heat safety below. HEAT SAFETY AND IMPACTS: By now youre well aware that it is going to be extremely hot this week with well-above normal temperatures; now lets talk about the impacts of excessive heat and actions we can take to minimize those impacts: With extreme heat, and especially prolonged heat events, it is a marathon, and not a sprint. Our bodies, infrastructure, pets, and livestock will be under duress from heat over the span of days as opposed to just a day or two. Given that there is little overnight relief expected throughout this event, this is where it really becomes a marathon, and precautionary measures are necessitated in order to prevent adverse results such as heat exhaustion and stroke. This is not just for individuals sensitive to heat, but rather, the entire population. Heat for this duration and at these temperatures can be dangerous for everyone. Do your body a favor and if you can, suspend outdoors activities between the hours of 10am and 7pm on days where Heat Advisories or Excessive Heat Warnings are in effect. Remain in air conditioning if you have that available to you in your residence, or seek out air conditioned environments such as stores, movie theaters, restaurants, libraries, and cooling shelters. If you cannot access air conditioned environments, must be outside, work outdoors, or otherwise, there are other precautionary measures you can take to keep yourself and your loved ones safe (including pets!) during excessive heat. Take frequent breaks in the shade and ensure that you are drinking plenty of cool water, or other hydrating beverages such as sports drinks with electrolytes. Avoid DEHYDRATING drinks such as alcohol or caffeinated beverages. That aside, visiting your city public pool or a lake, river, or ocean can also help keep you cool, but dont forget the life jacket! If planning on swimming, stick to where there is a lifeguard, and know the ocean or river conditions before you get in. Although outside of our area, its worth repeating: rivers can run fast and cold with snowmelt in the Sierra Nevada mountains, and cold water shock can set in quickly, which can lead to loss of muscle control, and ultimately, drowning. Cold water shock can also set in for ocean- goers. Have fun at the water, but be smart, be safe, and Know Before You Go! Finally, if you do not have air conditioning or cannot access it, and also cannot access a body of water to stay cool: consider taking cold showers or baths, turn on those sprinklers or garden hose and have a fun time in your own makeshift water park, or lay a damp, cool towel across your head or body. Even just dipping your hands and feet in cool water can help to abate feelings of excessive heat. For pets and livestock, make sure they have access to shade structures or areas, and have clean water freely available to them at all times. They do not have the same resources or ability to notify of feeling heat-stressed as we do, so check in on them! If theyre permanently outdoors, consider giving them a quick rinse- down with the hose or set up misters, as the evaporation will help to keep them cool as well. && .AVIATION... (06Z TAFS) Issued at 1029 PM PDT Mon Jul 1 2024 IFR-LIFR ceilings continue at the immediate coast south of HAF, with the only inland intrusion around the Monterey Bay region and into the northern Salinas Valley, expected to retreat to the coast Tuesday morning. Very low confidence in the development of stratus across the rest of the region tonight. Light winds tonight will develop into breezy onshore flow Tuesday afternoon. Marginal LLWS concerns continue during the overnight periods, especially at the coast and in the North Bay. Vicinity of SFO...High confidence of VFR through the TAF period. Light winds overnight, building to a breezy west-northwest flow on Tuesday afternoon with gusts up to 20-25 knots. Winds diminish in the evening. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...LIFR ceilings will impact the terminals through late Tuesday morning. Model output is showing visibility reductions sometime overnight but confidence in timing is low. Added a TEMPO group for visibilities below 1 SM based on persistence from the previous morning. Breezy northwest flow develops Tuesday afternoon, with ceilings returning to the terminals during the evening. && .MARINE... (Tonight through next Sunday) Issued at 1029 PM PDT Mon Jul 1 2024 Fresh to strong northerly winds with gale force gusts possible continue over the outer coastal waters into Tuesday. Winds will diminish and become moderate to fresh by mid-week as surface high pressure strengthens and moves eastward. In general, north to northwest winds prevail through the forecast period but wind direction may become more variable by late week as winds weaken. Elevated significant wave heights between 10-12 feet continue through mid-week before abating by the late week. Portions of the northern outer waters may see peak wave heights between 12-16 feet through mid-week. && .FIRE WEATHER... Issued at 330 PM PDT Mon Jul 1 2024 A Red Flag Warning will be in effect starting at 11pm tonight for some elevated locations in the North Bay Hills, East Bay Hills, Marin and Sonoma Coastal Ranges through late tomorrow evening with the North Bay Hills RFW continuing until 5pm Wednesday. RH values are generally in the teens with gusty north/northeast offshore flow. As the hot and dry pattern persists, fuels continue to dry. ERCs are drying in to the 70-90 percentile range across our region. Combine that with the expected surge of campers over the long holiday weekend and obvious risks of fireworks, putting our area in a combustible situation through next weekend. Fireworks should not be used this year, and campers should be very careful with anything dragging from trailers and securing campfires. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Coastal Flood Advisory until 11 PM PDT Wednesday for CAZ006-506- 508. Heat Advisory from 11 AM this morning to 7 PM PDT Wednesday for CAZ006. Red Flag Warning until 11 PM PDT this evening for CAZ502-503-512- 515. Excessive Heat Warning from 11 AM this morning to 8 PM PDT Sunday for CAZ502>504-506-510-512>518. Red Flag Warning until 5 PM PDT Wednesday for CAZ504. Heat Advisory from 11 AM this morning to 8 PM PDT Sunday for CAZ508-528-529. PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt Reyes 0-10 nm. Gale Warning until 3 AM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...DialH MARINE...Kennedy Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea